If you see taillights ahead while you are driving in fog:

Question

When driving under foggy conditions, lights cannot be taken as a reliable indication of where the road is. The lights may be coming from a vehicle that has pulled off the road.

Accepted Answer

The lights may not indicate where the road is as the vehicle may have pulled off the roadway.

Answer

You can assume the vehicle ahead is on the road.

Answer

It may be an optical illusion.